If you have load-share capable power supplies, and then use steering diodes on the outputs, then (in general, there may be exceptions, but I've never seen one) the power supplies can no longer load-share. For load share capable PSUs to load share, their outputs must be directly connected together.
This is because of the properties of a diode. A diode will only conduct when it is "forward biassed", which means that the anode is more positive than the cathode, and that voltage differential exceeds (silicon) 0.7v.
Which ever diode has the highest voltage source will reverse bias all the other diodes, so only one conducts.
This mechanism ensures that if you have two sources of power and a diode steering mechanism, the source with the higher voltage wins. Its a very neat and reliable answer to high availability power, fire and burglar alarm panels use steering diodes for just this purpose; if the mains is on, the power comes from the mains supply. If not, then the next source of power is the standby battery.